1. Field of Invention
The invention relates generally to the processing of semiconductor wafers, and relates more particularly to an apparatus for reducing entrapment of foreign matter along a moveable shaft of a substrate support.
2. Background of the Invention
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication techniques and processes. One fabrication process frequently used is chemical vapor deposition (CVD). Chemical vapor deposition is generally employed to deposit a thin film on a substrate or a semiconductor wafer.
Chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber. The precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on the surface of the substrate that is positioned on a heated substrate support (e.g., a heater) typically fabricated from aluminum. In some systems, the substrate support is mounted upon a moveable (e.g., moveable longitudinally, or rotatable) shaft that is disposed within a sleeve. Purge gas is routed through holes in the support to the edge of the substrate to prevent deposition at the substrate's edge that may cause the substrate to adhere to the support. Deposition by-products produced during the reaction are pumped from the chamber through an exhaust system.
In operation, particles or loose foreign matter may be generated by the system, or inadvertently introduced thereto, and these particles can travel within the confines of the chamber. In particular, particles may travel near the shaft utilized to control the elevation of a substrate support within the processing chamber. The particles may stick to the moving shaft and accumulate in the annulus, or gap, between the shaft and the sleeve that guides the shaft through the bottom of the chamber. The accumulation of particles between the shaft and sleeve can damage both components, leading to premature wear and/or failure of the system.
Reducing the annulus between the sleeve and the shaft is one method for minimizing the area in which particles may travel and/or become trapped. Although reducing the gap is a generally effective method for reducing particle accumulation and damage, a small gap still exists that is typically large enough to trap smaller particles. Alternatively, some designs have employed o-rings (sometimes in conjunction with a lubricant) positioned to seal the gap. However, standard o-rings are subjected to abrasion by particulates disposed on the shaft, and thus may not effectively seal the gap after a period of use. Furthermore, standard o-rings tend to generate particles when subjected to processing chamber conditions, exacerbating the particle entrapment problem rather than solving it.
Therefore, there is a need for an apparatus for reducing the entrapment of particles and foreign matter along a moveable shaft of a substrate support.